skip_bytes use File Seek

Currently for bytes skipping, tsMuxer reads 2 MB blocks at a time from the input file through a loop: this can take substantial time for large skips/files -especially when the file is on a NAS, accessed via WiFi.

This pull introduces file seeking so that only two blocks  (4MB) are left to be read.

Fixes issue #733.

tsMuxer/abstractReader.h

@@ -19,6 +19,7 @@ class AbstractReader
     AbstractReader() : m_blockSize(0), m_allocSize(0), m_prereadThreshold(0) {}
     virtual ~AbstractReader() = default;
     virtual uint8_t* readBlock(int readerID, uint32_t& readCnt, int& rez, bool* firstBlockVar = nullptr) = 0;
+    virtual bool incSeek(int readerID, int64_t offset) = 0;
     virtual void notify(int readerID, uint32_t dataReaded) = 0;
     virtual int createReader(int readBuffOffset = 0) = 0;
     virtual void deleteReader(int readerID) = 0;

tsMuxer/bufferedReader.h

@@ -94,7 +94,7 @@ class BufferedReader : public AbstractReader, TerminatableThread
     uint32_t getReaderCount();
     void terminate();
     void setFileIterator(FileNameIterator* itr, int readerID);
-    bool incSeek(int readerID, int64_t offset);
+    bool incSeek(int readerID, int64_t offset) override;
     bool gotoByte(int readerID, int64_t seekDist) override { return false; }
 
     void setId(const uint32_t value) { m_id = value; }

tsMuxer/ioContextDemuxer.cpp

@@ -87,15 +87,17 @@ unsigned IOContextDemuxer::get_buffer(uint8_t* binary, unsigned size)
     int readRez = 0;
     uint8_t* dst = binary;
     const uint8_t* dstEnd = dst + size;
+
     if (m_curPos < m_bufEnd)
     {
-        const unsigned copyLen = min((unsigned)(m_bufEnd - m_curPos), size);
+        const unsigned copyLen = min(static_cast<unsigned>(m_bufEnd - m_curPos), size);
         memcpy(dst, m_curPos, copyLen);
         dst += copyLen;
         m_curPos += copyLen;
         m_processedBytes += copyLen;
         size -= copyLen;
     }
+
     while (dst < dstEnd)
     {
         uint8_t* data = m_bufferedReader->readBlock(m_readerID, readedBytes, readRez);
@@ -104,43 +106,54 @@ unsigned IOContextDemuxer::get_buffer(uint8_t* binary, unsigned size)
 
         m_curPos = data + 188;
         m_bufEnd = m_curPos + readedBytes;
-        const unsigned copyLen = min((unsigned)(m_bufEnd - m_curPos), size);
+        if (readedBytes == 0)
+            break;
+        const unsigned copyLen = min(readedBytes, size);
         memcpy(dst, m_curPos, copyLen);
         dst += copyLen;
         m_curPos += copyLen;
         size -= copyLen;
         m_processedBytes += copyLen;
-        if (readedBytes == 0)
-            break;
     }
     return static_cast<uint32_t>(dst - binary);
 }
 
 void IOContextDemuxer::skip_bytes(const int64_t size)
 {
+    if (size == 0)
+        return;
     uint32_t readedBytes = 0;
     int readRez = 0;
     int64_t skipLeft = size;
-    if (m_curPos < m_bufEnd)
+
+    if (skipLeft < m_bufEnd - m_curPos)
     {
-        const int64_t copyLen = min(m_bufEnd - m_curPos, skipLeft);
-        skipLeft -= copyLen;
-        m_curPos += copyLen;
-        m_processedBytes += copyLen;
+        m_curPos += skipLeft;
+        m_processedBytes += skipLeft;
+        return;
     }
+
+    if (skipLeft > 2LL * m_fileBlockSize)
+    {
+        const int64_t offset = skipLeft - 2LL * m_fileBlockSize;
+        m_bufferedReader->incSeek(m_readerID, offset);
+        m_processedBytes += offset;
+        skipLeft = 2LL * m_fileBlockSize;
+    }
+
     while (skipLeft > 0)
     {
         uint8_t* data = m_bufferedReader->readBlock(m_readerID, readedBytes, readRez);
         if (readedBytes > 0 && readRez == 0)
             m_bufferedReader->notify(m_readerID, readedBytes);
         m_curPos = data + 188;
         m_bufEnd = m_curPos + readedBytes;
-        const int64_t copyLen = min(m_bufEnd - m_curPos, skipLeft);
+        if (readedBytes == 0)
+            break;
+        const int64_t copyLen = min(readedBytes, skipLeft);
         m_curPos += copyLen;
         m_processedBytes += copyLen;
         skipLeft -= copyLen;
-        if (readedBytes == 0)
-            break;
     }
 }
 

tsMuxer/metaDemuxer.h

@@ -121,6 +121,7 @@ class ContainerToReaderWrapper final : public AbstractReader
         m_terminated = false;
     }
     uint8_t* readBlock(int readerID, uint32_t& readCnt, int& rez, bool* firstBlockVar = nullptr) override;
+    bool incSeek(int readerID, int64_t offset) override { return false; }
     void notify(int readerID, uint32_t dataReaded) override {}
     int createReader(int readBuffOffset = 0) override;
     void deleteReader(int readerID) override;